1. Field of the Invention
The present invention relates to a solidifying material and a waste container suitable for the final disposal of radioactive wastes generated from a nuclear power plant and the like, a structure for disposal, a back-filling material, and a process for solidifying radioactive wastes.
2. Description of the Related Art
Hitherto, hydraulic inorganic solidifying materials such as cement and water-glass (sodium silicate) have been used for waste containers, solidifying materials, back-filling materials and structures for disposal site of so-called a low level radioactive waste such as a concentrated liquid waste, a spent ion exchange resin and various solids generated from nuclear power plants and nuclear fuel reprocessing facilities.
The above-mentioned hydraulic inorganic solidifying materials have the merits of (1) an easy operation, (2) an inexpensiveness and (3) an excellent radiation resistance and are suitable for disposal of low level radioactive wastes.
Furthermore, for a disposal of low level radioactive wastes, it is necessary that the solidifying materials can maintain safety even under such a condition that solidifying materials or disposal facilities sink under the water and besides can greatly retard leakage of internal radioactive nuclides out of the waste forms or disposition facilities.
A conventional method for assuring long-term endurance of waste forms is to add glass fibers to hydraulic solidifying materials as described in Japanese Patent Kokai (Laid-Open) No. 60-202398. Since fibrous materials have tensile strength several times that of the base hydraulic solidifying materials, they have a reinforcing effect to remarkably improve tensile strength and flexural strength of the whole waste form. Therefore, even if the waste form undergoes a change in volume of the filler or is applied with an external force, cracks or breakage of the waste form do not occur and even in the case of the waste form being disposed into the land, it is considered that the waste form can never deteriorate during from several ten years to several hundred years in which radioactivity decays to sufficiently low level.
Furthermore, for retardation of leakage of radioactive nuclides, Japanese Patent Kokai (Laid-Open) No. 58-40000 has proposed to provide a protective layer for a waste container for radioactive wastes and to embed a filler having ion exchangeability and adsorbability in this protective layer.
Among the above-mentioned conventional methods, the method described in Japanese Patent Kokai (Laid-Open) No. 60-202398 does not consider reduction of leaching rate of radioactivity from wastes and has the problem that a countermeasure to reduce leaching rate of radioactivity is required when wastes higher in level of radioactivity than the present level are disposed of or when wastes containing carbon-14 or technetium-99 longer in half-life are disposed of.
On the other hand, since the invention disclosed in Japanese Patent Kokai No. 58-40000 has not the property to improve the strength of the waste container, the invention has a problem that cracks occur in the waste container due to the cycles of dry/wet and hot/cold of the disposal site, and hence the maintenance of soundness thereof is impossible.